Rashi comments on the repetition of the word “shono” in the ages of both Soroh Braishis 23 (1) and Avrohom Braishis 25 (7). Why is there no comment for the age of Yishmoel which also repeats “shono” Braishis 25 (17).
We find 4 ways in which the amount of years they lived are presented:
(Breshit 5:6 onwards) From Sheth to Noach (Including Noach): "And all their days were..."
(Breshit 25:17) Yishmael: "And the years of his life were..."
None of these have anything special that invites a question. You may ask why the change between days and years but we saw Rashi in Breshit 24:25 that days may mean a year.
(Breshit 23:1) Sarah: But when we see the pasuk about Sarah it says after giving the amount ".. the days of her life." This addition asks for an explanaition ("Omer darsheni"), which is why Rashi explained what he did.
(Breshit 25:7) Avraham: Here too we see an addition: "The days ot the years of Avraham's life which he lived.." which Rashi felt had to be explained.
Now the repetition of the word "years" following the units is a common way of saying it, maybe to teach us that the years of someone's life are not just a number.
The Chumas Shai LeMorah on Bereshit 25:7 brings a Levush Ha'Orah who says that Rashi is actually learning from the words "Which he lived" (as rony pointed out). He says that "Which he lived" implies that all his years were equally good, which is problematic to Rashi since the Midrash tells us that Avraham's youth was troubled. He spent many years in jail and was thrown into a fiery furnace. Therefore Rashi tells us that his life was equal with regards to sin that throughout Avraham's life he was free from sin.
If so, we have no question as to why the years are repeated by Yishmael, since we aren't learning from that.
The Chumas Shai LeMorah then quotes an alternative answer from the Maskil LeDavid (on the beginning of the Parsha) who explains how we could be learning out from the repetition of the word "shana". The Maskil Ledavid points out that according to some opinions, Avraham didn't recognize his Creator until 48. If so, how can you say all his years were equally without sin. Rather, once Avraham did Teshuva out of Love for G-d, all his sins were converted to merits, and it was as if he never sinned.
Rashi later tells us that Yishmael did Teshuva (Bereshit 25:9), so once Rashi tells us that Yishmael did Teshuva, we don't need him to explain why the Torah repeats "shana" by Yishmael, since we can understand that once he did Teshuva all his sins were converted to merits and all his years can now be equated.
I didn't actually look up these commentaries inside.
According to the Maharshal (cited in the Sifse Chachamim), Rashi does comment on the repetition of shana, though implicitly: it's because of the repetition of shana that we know to use the pasuk for the d'rasha that Rashi cites.
(I don't understand why the repetition of shana is necessary for that — why couldn't we make the d'rasha without the repetition of shana? — but that's what the Maharshal seems to be saying.)
The question remains why Rashi doesn't explicitly say he's commenting on the repetition of shana.